The present invention is directed to integrated circuits, and more particularly to interconnection of integrated circuits and other components.
An integrated circuit (IC) is a small device with tiny contact pads that must be connected to other circuitry to form a complete system. ICs and other circuits are often interconnected through intermediate substrates such as printed circuit boards (PCBs) or interposers. An IC's contact pads can be connected to the substrate's contact pads by discrete wires. However, to reduce the size of the assembly and shorten the electrical paths, the discrete wires can be eliminated, as illustrated in FIG. 1.
FIG. 1 shows two ICs 110.1, 110.2 connected to each other and possibly to other circuits through an interposer 120 and a PCB 124. In this example, each IC 110 (i.e. 110.1 and 110.2) is a “die” (also called “chip”), i.e. it is initially manufactured in a semiconductor wafer (not shown) together with other ICs, and the wafer is then cut up to separate the ICs. The interposer includes a support 120S with conductive vias 130 passing through the support. The interposer also includes a redistribution layer (RDL) 140 with conductive lines 140L insulated from each other by dielectric 140D. (The conductive lines may be arranged as one or more conductive layers; if there is only one conductive layer, the conductive lines can be horizontal, without vertical portions.) The dies' contact pads 110C are attached to contact pads 120C.T provided at the top of RDL 140.T. The connections are shown at 144, and can be solder, adhesive, diffusion bonding, or some other type. Discrete wires can also be used. The RDL's conductive lines 140L interconnect the contact pads 120C.T and the vias 130. The vias terminate at the bottom at contact pads 120C.B. Contact pads 120C.B are attached to the PCB's contact pads 124C with other connections 144, e.g. solder or adhesive or diffusion bonding. The PCB may include other contact pads connected to other circuits (ICs, interposers, or other components, not shown). The PCB's conductive lines 124L interconnect the PCB's contact pads 124C as needed.
PCB 124 and interposer 120 absorb and dissipate some of the heat generated by the die and thus reduce thermal stresses (mechanical stresses resulting from thermal expansion). Also, if the interposer's coefficient of thermal expansion (CTE) is intermediate between the PCB and the die, then the interposer may alleviate some of the stresses arising from the CTE mismatch between the die and the PCB. Further, the PCB manufacturing technologies may not allow the PCB contact pads 124C to be as densely packed as the die's contact pads 110C, and in this case the interposer 120 serves to “redistribute” the contact pads, i.e. provide the interconnection despite the positional mismatch between the die's and PCB's contact pads.
The vias 130 can be formed by depositing metal into through-holes made in support 120S. However, it is often preferred that the through-holes be narrow (in order to reduce the lateral area of the structure), and metal deposition into narrow holes is complicated, resulting possibly in metal discontinuities and voids which impair electrical conductivity and reliability. To address this problem, the fabrication process can be reversed: vias 130 can be initially formed as free-standing posts on a sacrificial substrate 210 (FIG. 2A), and these posts can then be inserted into through-holes 148 in a separate support 120S (FIGS. 2A, 2B). Substrate 210 can then be removed (FIG. 2C). See U.S. Pat. No. 7,793,414 issued Sep. 14, 2010 to Haba et al. Posts 130 can be formed by deposition and etch or by a selective deposition process. Selective deposition processes include electroplating, chemical vapor deposition (CVD), evaporation, sputtering, and printing.
It is desirable to provide improved processes and materials for forming interconnections.